Wells of this type are known from documents EP-A-0 325 874 and WO-A-03/065047, and are used for determining the time required for the physical state of a medium to change, in particular for determining the coagulation time of a blood sample, each well being open at its top end and including a circularly arcuate bottom forming a track for a ferromagnetic material ball that can be caused to move in the well in periodic motion by means of an external magnetic field, variations in amplitude and/or frequency of the motion of the ball being representative of the physical state of the blood sample.
In document WO-A-03/065047, the wells containing the balls are fastened side by side in a detachable manner on a flexible support film that closes their top ends and that can be wound on a reel in order to feed an automatic analysis appliance and cause the wells to move in succession through the appliance.
That film includes a series of slots or orifices situated in register with the well openings for depositing samples and reagents into the wells.
In order to fasten the wells onto the film, each well includes, at its top end, two lateral tabs formed with protruding studs designed to be engaged by force in lateral perforations of the film, the tabs of the wells fastened to the film forming a rack enabling the film and well assembly to be driven by meshing with a cog belt or the like.
Those known means present numerous advantages but also a few drawbacks:                the wells must be fastened to the film, and then removed from said film after use, which operations are not always carried out in a perfect manner, with risk of premature or late removal of the wells. Those operations also represent a cost that is not negligible relative to the cost of the wells and that is in addition to the cost of the film to which the wells are fastened;        while the wells are being moved, the balls contained therein might be poorly retained by the film and they might be ejected from the wells. In this event, the planned analyses cannot be performed correctly in the wells and must be re-done in wells containing balls, and that results in a loss of samples, of reagents, and of time.        